Author(s): L. Goffin; P. Archambeau; M. Pirlotton; S. Erpicum; B. Dewals

Linked Author(s): Benjamin J. Dewals, Sébastien Erpicum

Keywords: Dam removal; Riverbed stability; Threshold channels; Hydrodynamic modeling

Abstract: An operational procedure to assess the stability of riverbeds after dam removal has been developed. It combines hydrodynamic simulations with statistical analysis and mapping of bed stability parameters. The method is demonstrated on a case study in the French Alps. Dam removal may lead to long-term ecological benefits including improved fish passage, increased biodiversity and recovery of sediment continuity. However, removing a dam may trigger substantial geomorphic evolutions, which in turn may endanger buildings and infrastructures situated on the riverbanks. Therefore, the dam removal works must be carefully designed so that river incision and bank instabilities are avoided at critical locations, and that appropriate mitigation measures are implemented to control the extent of bed and bank erosion. In principle, morphodynamic modeling could be used to inform the design of the dam removal works. Nevertheless, in many situations, this is hardly feasible due to multiple reasons, such as the lack of data on sediment supply upstream, the absence of validation data (e.g., historic riverbed profiles) and the complexity of the process involved (e.g., role of large boulders, which cannot be described as a continuous medium). Here, we present an original method which uses detailed 2-D hydraulic simulations to extract valuable information for assessing the post-dam-removal stability of riverbed, both globally (i.e., at the reach level) and locally (i.e., in the near field of the removed dam). A remarkable case study is used to illustrate the application of our method. Carried out by Electricite de France (EDF), it consists in the replacement of five one-century-old hydropower schemes by a single one, more powerful and more environmentally friendly. Public authorities request that EDF considers the (partial) removal of five existing dams, which will not be used anymore in the new project.

DOI: https://doi.org/10.3850/978-981-11-2731-1_185-cd

Year: 2018